In an integrated circuit, the transistors are formed within and on an active semiconductor region, for example silicon, surrounded by an electrically-insulating region, for example a trench filled for example with silicon dioxide, in particular of the shallow trench isolation (or STI) type.
The formation of an MOS transistor inside of an insulating region may (depending on the thermal expansion coefficient of the insulating material and on the deposition temperature) lead to the formation of an active region with compressive stress owing to the presence at its periphery of the insulating region.
Although an active region with compressive stress favors the performance characteristics of a PMOS transistor in certain directions, notably in terms of mobility of the carriers, there exists a need to further improve these performance characteristics, notably in terms of mobility.